Press for making a shaped workpiece

ABSTRACT

A press for compacting a soft mass into a shaped workpiece. The press has a die adapted to hold the soft mass and having an open side, a compacting tool displaceable along an axis through the side into the die to compact the mass therein, a cylinder centered on the axis adjacent and outside the die, a piston shiftable in the cylinder along the axis and connected to the compacting tool, a relatively movable guide formation outside the die, offset from the axis, and fixed to the piston, a second guide formations fitting with the first formation, outside the die, offset from the axis, and generally stationary relative to the piston. The formations having engaging surfaces extending parallel to the axis, and actuator for displacing the piston axially into the die and thereby compact the mass therein. The guide-formation surfaces sliding axially relative to each other on axial displacement of the piston.

FIELD OF THE INVENTION

The present invention relates to a press for making a shaped workpiece. More particularly this invention concerns a so-called powder press that serves to compact a mass of powder or the like into a complexly shaped workpiece.

BACKGROUND OF THE INVENTION

In the production of complexly shaped workpieces it is known to start with a mass of loose powder, a sort of paste formed by powder mixed with a liquid binder, or even a preshaped but relatively soft workpiece and to compact it in a press into a final shape. Subsequently the pressed workpiece is often cured, for example by sintering, to a final hardness, and is in some situations subjected to final machining-milling or boring-operations on selected surfaces.

Such a press typically has a die for holding the soft mass to be shaped and a compacting tool that is part of or connected to a piston/cylinder unit. To obtain the desired workpiece shape, the tool is shifted by the respective one piston/cylinder unit along a central axis into the die.

A press of this type makes it possible to fabricate shaped workpieces made of metal powder by pressing and subsequent sintering. To this end at least one compacting tool is required that is introduced into the die. In this case, the die has a cavity that is open to the side of the tool. The die opening is closed by the tool except for a small clearance. When introduced into the die cavity, the tool builds up the pressure required for compressing the soft powder mass, paste, or preformed workpiece.

It is also possible for multiple tools to be provided that can move in one axial direction. In this case, the tools can be introduced into a die that is axially closed at one side or come from both axial directions in the case of a die that is axially open in both directions. In certain cases, a through-going mandrel serving mainly as an abutment to create a hole in the finished workpiece. The tools can also be introduced from the side into the die for generating undercuts or other shapes. For demolding the workpiece, the laterally introduced tools are retracted before the workpiece is pulled axially out of the die.

The tools are carried as mentioned above on respective piston/cylinder units. In some systems that produce complexly shaped or stepped workpieces a number of pistons are arranged concentrically to one another. During the pressing operation they are moved along a defined displacement trajectory relative to the respective cylinders according to the desired shape of the shaped workpiece.

In the solutions known from the prior art, the individual tools that are designed as pistons are guided in the respective cylinders by the piston abutting the respective bore of the cylinder with its outer cylindrical surface bearing radially outward on an inner cylindrical surface of the cylinder it slides in. Here, it has been found in particular in the fabrication of asymmetrically shaped workpieces that tilting moments whose axes are perpendicular to the central axis of the tool can create problems. The guiding of the pistons in the respective cylinders in this case no longer is sufficient for a high quality fabrication. Additionally, problems can occur if the rotationally symmetrical pistons in the cylinders can rotate about the central axis in an uncontrolled manner. The known tools of the structure in this case are not sufficient for assuring a sufficiently exact guiding of the pistons in the respective cylinders.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide an improved press for making a shaped workpiece.

Another object is the provision of such an improved press for making a shaped workpiece that overcomes the above-given disadvantages, in particular that ensures smooth guiding with no possibility of rotation of the compacting tools.

SUMMARY OF THE INVENTION

A press for compacting a soft mass into a shaped workpiece. The press has according to the invention a die adapted to hold the soft mass and having an open side, a compacting tool displaceable along an axis through the side into the die to compact the mass therein, a cylinder centered on the axis adjacent and outside the die, a piston shiftable in the cylinder along the axis and connected to the compacting tool, a relatively movable guide formation outside the die, offset from the axis, and fixed to the piston, a second guide formations fitting with the first formation, outside the die, offset from the axis, and generally stationary relative to the piston. The formations having engaging surfaces extending parallel to the axis, and actuator for displacing the piston axially into the die and thereby compact the mass therein. The guide-formation surfaces sliding axially relative to each other on axial displacement of the piston.

Thus, the invention proposes guiding means that are not known in the prior art that are at least partially situated at a certain spacing from the central axis.

The guiding means is preferably adapted for resisting a tilting moment between the cylinder and the piston, such tilting moment being perpendicular to the central axis, either radial or tangential. Especially in the case of asymmetrical shaped workpieces to be pressed, and for this reason, a symmetrical force distribution will inherently be created. The guide formations according to the invention ensure that no relative tilting between the piston and the cylinder can occur.

In a preferred embodiment of the invention the guide formations include at least one rod that is fixedly attached to the piston or the cylinder and that is guided in the cylinder or in the piston. In this embodiment, it is in particular advantages when multiple rods are provided on the piston or on the cylinder. This way for example four rods are used that are provided on the piston or on the cylinder. These four rods can be provided symmetrically to two planes that are perpendicular to each other.

The rod can be attached to a support that is attached to the piston or the cylinder. This support can be a plate extending perpendicular to the center axis.

Preferably, a number of piston/cylinder units are provided along the central axis. The pistons can be concentric to each other and at least two pistons can slide on each other on two surface areas facing each other. The guide formations basically can also slidable support multiple pistons and/or cylinders relative to each other.

The tool can be removable from the actuator of the press.

With the design according to the invention, pivoting of the piston relative to the respective cylinder is not possible, which is in particular important when non-symmetrical shaped workpieces are being pressed.

Furthermore, an improved guiding between piston and cylinder is achieved, in particular in the case of tilting moments being present between these two components, wherein the moment axis is perpendicular to the central axis of the piston/cylinder units.

The individual pistons of the tool are advantageously guided in an improved manner, in particular concerning their parallelism. The directional stability of the pistons as well is improved.

Finally, it is advantageous that the accessibility of the guiding elements has improved, since these are now outside the die and offset outward from most of the moving press elements.

It is further advantageous that less time is required for setup, since complicated dismounting of individual pistons for the purpose of improvement of the guide tolerance is avoided. The guide rods can be installed or removed quickly and easily, as well as the guide bushes for the rods. As a result the quality of the shaped workpiece is improved, since the tool is provided with parts precisely adapted to each other.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a small scale side view of the press according to the invention;

FIG. 2 is an axial section through a piston/cylinder and tool assembly of the invention;

FIGS. 3 a, 3 b, and 3 c are top views of the cylinder, piston, and support of the piston-cylinder unit, respectively;

FIGS. 4 a, 4 b, and 4 c are top views of the elements of another guide system for another of the piston-cylinder units; and

FIG. 4 d is a section taken along line IVd-IVd of FIG. 4 a.

SPECIFIC DESCRIPTION

As seen in FIG. 1 a press 1 for fabricating a shaped workpiece from a mass 12 of metal powder. Instead of such a mass 12, a paste, or a preformed workpiece could be treated with the press 1 according to the invention. Often, an already preformed workpiece is pressed in a further step, in particular in the final pressing where higher pressures are applied.

The press 1 substantially consists of a tool assembly 2 that can be inserted into a press-actuating device 3. The device 3 has a machine frame 13 with an upper cross bar 14 and a lower cross bar 15. On the upper cross bar 14, an upper piston 16 is provided in a cylinder by means of which a downwardly directed pressing force can be applied. The lower cross bar 15 has a lower piston 17 by means of which an upwardly directed pressing force can be applied.

The tool 2 has a die 18 that holds the powder mass 12. To made a desired shape in the workpiece, a number of tool-like pistons 5 provided concentrically to each other are provided that are arranged in respective cylinders 4 and can be displaced relative to these cylinders 5 in a controlled manner. Each piston 5 forms a piston/cylinder unit with the respective cylinder 4 surrounding and slidably receiving it. All the pistons 5 and cylinders 4 are concentric to a central axis 6 in the illustrated embodiment. By actuation of the respective piston/cylinder units 4, 5, a displacing movement in direction V (in the present case corresponding to the vertical direction) can be effected. Further tools 19 and 20 can be actuated by means of the upper piston 16, as well as a filling element 21 for loading the die 18 with the powder mass 12.

To ensure guiding without tilting of the pistons 5 relative to the cylinders 4 in case of asymmetrical workpieces and to further avoid a relative rotation between piston 5 and cylinder 4 about the central axis 6, the structure of FIG. 2 is provided. More particularly, between the piston 5 and the cylinder 4, guide formations 7 are provided that prevent tilting and pivoting. To this end, a support plate 11 is attached to the piston 5 on which in turn four parallel rods 9 of circular cross-section are firmly attached. The rods 9 are slidable in guides 10 in the cylinder 4 in the displacement direction V. The guides 10 can be sliding bushes with narrow tolerances that assure that in the event of a displacement of the piston 5 relative to the cylinder 4 in displacement direction V, a high level of parallelism of both elements 4, 5 is maintained. Notably, tilting moments M that are applied perpendicular to the displacement direction V will not have an impact on the parallelism of the piston 5 and cylinder 4. The rods 9 are positioned such that their axes 8 lie at the same radial spacing a from the central axis 6.

As it can be seen in the FIGS. 3 a to 4 d for two piston/cylinder units 4, 5 of the tool 2, in the present case, four rods 9 are provided that are oriented symmetrically to two mutually perpendicular symmetry planes. The rods 9 are fixed in the respective supports 11 that are in turn fixed to the piston 5.

Insertion of the guide rods 9 into the cylinder 4 enables the system to absorb off-center forces in a more efficient manner than hitherto possible, since the guide rods 9, due to their rigidity and their positions, can absorb and transmit torque and lateral forces in a more efficient manner than in the solution known from the prior art. These rods thus replace the typically provided guide strips that are not as efficient as the design according to the invention. 

1. A press for compacting a soft mass into a shaped workpiece, the press comprising: a die adapted to hold the soft mass and having an open side; a compacting tool displaceable along an axis through the side into the die to compact the mass therein; a cylinder centered on the axis adjacent and outside the die; a piston shiftable in the cylinder along the axis and connected to the compacting tool; a relatively movable guide formation outside the die, offset from the axis, and fixed to the piston; a second guide formations fitting with the first formation, outside the die, offset from the axis, and generally stationary relative to the piston, the formations having engaging surfaces extending parallel to the axis; and actuating means for displacing the piston axially into the die and thereby compact the mass therein, the guide-formation surfaces sliding axially relative to each other on axial displacement of the piston.
 2. The press defined in claim 1 wherein the second formation is braced and nondisplaceable transversely of the axis.
 3. The press defined in claim 1 wherein one of the formations is an axially extending rod and the other of the formations fits around the rod.
 4. The press defined in claim 3 wherein one of the surfaces is a plurality of the rods spaced about the axis.
 5. The press defined in claim 4 wherein there are four of the rods.
 6. The press defined in claim 3 wherein the one formation includes a support extending transversely of the axis and fixed to the rods.
 7. The press defined in claim 1 wherein there are a plurality of pistons and respective cylinders oriented coaxially of each other and provided with respective first and second guide formations.
 8. The press defined in claim 7 wherein one of the pistons is a sleeve coaxially surrounding and slidable on another of the pistons.
 9. The press defined in claim 7 wherein at least one of the second formations is fixed on one of the pistons.
 10. The press defined in claim 1 wherein the compacting tool and die are separable from the actuating means. 